Parenteral nutrition (PN) is often required to manage short bowel syndrome (SBS). The long term objective is to understand the mechanisms by which enteral and parenteral nutrients stimulate the neuroendocrine system to produce functional adaptation to bowel resection that permits oral feeding. Aim 1 will use a well-characterized rat resection model (60% jejuno-ileal resection + cecectomy) that mimics human SBS resulting in intestinal failure and requires PN for survival. The focus is to introduce enteral nutrients (semi-elemental, whey protein, liquid diet) in rats with SBS given PN in combination with a low dose of glucagon-like peptide-2 (GLP-2) to optimize intestinal adaptation, and to identify the underlying mechanisms. Aim 1 will test the hypothesis that early introduction of GLP-2 and enteral whey protein after intestinal resection will promote expansion of intestinal progenitors and stem cells and enhance absorptive function resulting in increased length and diameter of residual bowel such that independence from PN is achieved. Intestinal adaptive growth will be assessed by changes in cellularity, proliferation, apoptosis and histomorphometry. Intestinal cell lineages will be assessed by IHC, putative stem cells using flow cytometry and beta-catenin expression, and crypt fission by morphology. The associations between intestinal growth and GLP-2 and insulin-like growth factor-I (IGF-I) responses will be assessed by quantifying the relative abundance of proglucagon, GLP-2 receptor, IGF-I, and IGF binding proteins (IGFBP) mRNAs by RT-qPCR and by localizing of GLP-2 receptors using IHC. Aim 2 will test the hypothesis that IGF-I, IGFBP -3 and -5, and ErbB ligands/effectors mediate GLP-2- induced intestinal growth. Aim 2 will use knockout mice with deletion of IGFBP-3 and -5 treated in a 3x2 design with growth factor - vehicle, GLP-2 or IGF-I - and diet - whey or casein - to determine if enteral whey protein potentiates the intestinotrophic action of endogenous or exogenous GLP-2 independent of IGFBPs. The associations between intestinal growth and upregulation of ErbB ligands, proglucagon and IGF-I expression and GLP-2 levels will be determined. Subepithelial myofibroblasts will be isolated from jejunum of IGFBP-3/-5 knockout mice and treated with GLP-2 to determine if reduced IGF-I expression (mRNA &peptide) is one mechanism by which GLP-2 action is dependent on IGF-I. Mice given proximal resection of the small bowel with oral feeding will be used to determine if resectioninduced intestinal growth is dependent on expression of IGFBP-3/-5 and/or ErbB ligands.